Synchronous data link signal generator

ABSTRACT

A synchronous data link signal is generated for supply between digital television equipment in a studio and an RF transmitter. The synchronous data link signal includes first data to be encoded at a first data rate, second data to be encoded at a second data rate less than the first data rate, and a map defining the relative amounts and placement of the encoded first and second data in the synchronous data link signal. The first data is in the form of first output data packets of a predetermined size. The second data and the map data are multiplexed so as to provide more than one second output data packet having the predetermined size. The first and second output data packets are then multiplexed so as to provide the synchronous data link signal.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the generation of a synchronous datalink signal. For example, this synchronous data link signal may bearranged to comply with the format specified by the SMPTE 310M standard.

BACKGROUND OF THE INVENTION

The ATSC digital television standard presently provides for thetransmission of successive data transmission fields each comprising 313segments extending over a 24.2 ms time interval. FIG. 1 discloses anexemplary format for a data transmission field according to thisstandard. The first segment of each transmission field is a field syncsegment. The field sync segment is composed of four two-level segmentsync symbols and space for 828 other two-level symbols. A portion ofthis space is used for a field sync, and another portion of this spaceis reserved. Each of the remaining segments of each transmission fieldcomprises four two-level segment sync symbols and 828 n-level datasymbols where n is currently eight, although n could be other integerssuch as two, four, sixteen, etc.

As indicated by U.S. patent application Ser. No. 09/804,262 filed onMar. 13, 2001, there is presently some interest in extending the ATSCdigital television standard to allow a transmission field to contain amix of more robustly coded data (referred to herein as E-VSB data) andthe data currently provided for in the standard (referred to herein asVSB data). Preferably, although not necessarily, the data mix isemployed on a segment-by-segment basis such that some segments of atransmission field are used to transmit VSB data exclusively and theremaining segments of the transmission field are used to transmit E-VSBsegments exclusively. However, it is possible that all data segments ofa transmission field could contain either E-VSB data segmentsexclusively or VSB data segments exclusively. Moreover, it is alsopossible that the E-VSB data contained in some segments of atransmission field may be coded at one robust coding rate and that theE-VSB data in other segments of the transmission field may be coded atother robust coding rates.

As disclosed in the above mentioned '262 application, a map thatindicates which segments contain the more robust (E-VSB) data and whichsegments contain standard VSB data is preferably provided by thetransmitter to the receiver so that the receiver can properly decode andotherwise process the received VSB and E-VSB data. Assuming that atransmission field contains E-VSB data at different coding rates, themap in that case must also designate the coding rates that apply to thedifferently coded E-VSB data segments.

The '262 application describes one mapping system. U.S. patentapplication Ser. Nos. 10/011,333 and 10/011,900 filed on Dec. 3, 2001,describe another mapping system that reliably identifies which segmentscontain VSB data and which segments contain E-VSB data.

Moreover, SMPTE 310M is a standard that specifies a synchronous serialinterface for MPEG-2 digital transport streams between studio equipment(such as multiplexer's, encoders, decoders, ATM gateways, fiber opticinterfaces, etc.) and an RF transmitter. The SMPTE 310M standard definesparameters for digitally transmitting the MPEG-2 digital transportstream with a transfer rate of 19.4 or 38.8 Mbits/sec and is primarilyused for digital television applications.

E-VSB data and VSB data could be transferred between studio equipmentand an RF transmitter using separate lines or channels. However, whenE-VSB data and VSB data are to be combined in a field along with the mapdata that denotes the locations of the E-VSB data and VSB data withinthe transmission field, it is more desirable to multiplex the databetween the studio equipment and the RF transmitter over a single lineor channel.

Accordingly, one embodiment of the present invention is directed to acombination of E-VSB data, VSB data, and map data so as to provide asynchronous data link signal. This synchronous data link signal can thenbe transmitted over a single line or channel. In one exemplaryimplementation of this embodiment of the present invention, thissynchronous data link signal can be arranged to meet the SMPTE 310Mstandard.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a methodprovides a synchronous data link signal that includes first data to beencoded at a first data rate, second data to be encoded at a second datarate less than the first data rate, and map data defining the relativeamounts and placement of the encoded first and second data in thesynchronous data link signal. The method comprises the following:providing the first data in the form of first output data packets of apredetermined size; multiplexing the second data and the map data toprovide more than one second output data packet having the predeterminedsize; and, multiplexing the first and second output data packets toprovide the synchronous data link signal.

In accordance with another aspect of the present invention, anelectrical synchronous data link signal comprises first data packets andsecond data packets. Each of the first data packets has a predeterminedsize, and each of the second data packets has the predetermined size.Each of the first data packets contains first data to be encoded at afirst data rate, each of the second data packets contains second data tobe encoded at a second data rate less than the first data rate, and atleast one of the second data packets includes place holding data. Thefirst and second data packets are multiplexed in the electricalsynchronous data link signal.

In accordance with still another aspect of the present invention, amethod provides a synchronous data link signal including first data tobe encoded at a first data rate, second data to be encoded at a seconddata rate less than the first data rate, and map data defining therelative amounts and placement of the first and second data in an SDLframe. The method comprises the following: providing the first data inthe form of first output data packets of a predetermined size;multiplexing the second data and the map data to provide more than onesecond output data packet having the predetermined size; adding a headerto each of the second output data packets; and, multiplexing the firstand second output data packets to provide the synchronous data linksignal, wherein the header uniquely identifies one of the second outputdata packets.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages will become more apparent from adetailed consideration of the invention when taken in conjunction withthe drawings in which:

FIG. 1 illustrates an exemplary format for a data field according to theATSC digital television standard;

FIG. 2 illustrates a VSB/E-VSB system in accordance with an embodimentof the present invention;

FIG. 3 illustrates a multiplexer that can be used in the VSB/E-VSBsystem shown in FIG. 2;

FIG. 4 illustrates an E-VSB preprocessor that can be used in multiplexershown in FIG. 3;

FIG. 5 illustrates exemplary first and subsequent E-VSB segments of afield produced by the VSB/E-VSB system of FIG. 1; and,

FIG. 6 illustrates an exemplary arrangement of segments contained in thesynchronous data link signal provided by the multiplexer of FIG. 3.

DETAILED DESCRIPTION

A VSB/E-VSB system 10 is shown in FIG. 2 as an exemplary embodiment ofthe present invention. The VSB/E-VSB system 10 includes a VSB server 12and an E-VSB server 14 coupled to a multiplexer 16. The VSB server 12supplies VSB data to the multiplexer 16, and the E-VSB server 14supplies E-VSB data to the multiplexer 16.

A controller 18 controls the VSB server 12 and the E-VSB server 14 inaccordance with a map to supply the VSB data and the E-VSB data at thecorrect points in time so that the multiplexer 16 correctly formats thedata for supply over a serial synchronous data link 20 to an RFtransmitter 22. Thus, the controller 18 controls the multiplexer 16 inaccordance with the map so that the multiplexer 16 multiplexes the VSBdata and the E-VSB data in accordance with the map. Moreover, thecontroller 18 also supplies the map to the multiplexer 16 for inclusionin the serial synchronous data link signal that the multiplexer 16supplies over the serial synchronous data link 20 to the RF transmitter22. The RF transmitter 22 may include, for example, a VSB modulator, adigital filter, a VSB/E-VSB encoder, an SMPTE 310 receiver, etc.

As shown in greater detail in FIG. 3, the multiplexer 16 includes a lowvoltage digital signal receiver 30 that receives VSB data packets fromthe VSB server 12, and a low voltage digital signal receiver 32 thatreceives E-VSB data packets from the E-VSB server 14. The VSB datapackets supplied by the VSB server 12 are typically standard 188 bytepackets. The packets supplied by the E-VSB server 14 are also 188 bytepackets.

The VSB data packets from the low voltage digital signal receiver 30 arebuffered by a VSB packet buffer 34, and the E-VSB data packets from thelow voltage digital signal receiver 32 are buffered by an E-VSB packetbuffer 36. The VSB packets stored in the VSB packet buffer 34 aresupplied directly to a mux 38. However, the E-VSB packets stored in theE-VSB packet buffer 36 are processed by an E-VSB preprocessor 40 asdescribed below.

The multiplexer 16 shown in FIG. 3 assumes that E-VSB data will beprovided at a single robust coding rate. If E-VSB data at other codingrates are to be included in the synchronous data link signal supplied tothe RF transmitter 22, an additional low voltage signal receiver, E-VSBpacket buffer, and E-VSB preprocessor may be included in the multiplexer16 for each of such other coding rates.

As shown in FIG. 4, the E-VSB preprocessor 40 includes a byte splitter48 that splits the E-VSB data from packets of 188 bytes to packets of164 bytes. Accordingly, for every forty-one 188 byte packets supplied asan input to the byte splitter 48, the byte splitter 48 provides anoutput of forty-seven 164 byte packets. A Reed/Solomon encoder 50 of theE-VSB preprocessor 40 adds 20 Reed/Solomon bytes to each 164 bytes ofdata that the Reed/Solomon encoder 50 receives from the byte splitter48. An interleaver 52 interleaves the output of the Reed/Solomon encoder50. The interleaver 52 may be similar to the interleaver disclosed inthe ATSC digital television standard and may be arranged so that B=46,M=4, and N=184. A header inserter 54 receives the interleavedReed/Solomon encoded E-VSB data and performs a number of functions.

The header inserter 54 inserts a header from the controller 18 at thebeginning of each E-VSB packet. The header includes a synchronizationbyte and three bytes which identify the packets as E-VSB packets. Thesethree bytes also designate which packet is the first E-VSB packet to beinserted in an SDL frame, and which packets are subsequent packets in anSDL frame. The SDL frame is shown in FIG. 6 and is discussed below.

The header inserter 54 further inserts an odd/even field flag byte fromthe controller 18 after the header. The odd/even field flag designateswhether the packet is to be inserted into an odd transmission field oran even transmission field, adds the map that preferably comprises threebytes and that is supplied by the controller 18, and stuffs the E-VSBdata with place holder bits. These place holder bits, for example, aredesignated to be zero bits.

Accordingly, the first E-VSB packet is shown in FIG. 5 as a first E-VSBpacket 60. The first E-VSB packet 60 includes the header describedabove. This header, for example, may be 32 bits. The first byte of thisheader comprises a synchronization byte, and the three remaining bytesof this header comprise a PID designating the packet as an E-VSB packetand further designating the packet as the first E-VSB packet to beinserted in the transmission field of FIG. 1. The remainder of the firstE-VSB packet 60 includes 736 bits of E-VSB data interspersed first withthe odd/even field flag byte, second with the three byte map, and thirdwith place holder bits.

Thus, the first sixteen bits following the header comprise, in order,the first E-VSB data bit E-VSB0, the first odd/even field flag bit, thesecond E-VSB data bit E-VSB1, the second odd/even field flag bit, . . ., the eighth E-VSB data bit E-VSB7, and the eighth odd/even field flagbit. The odd/even field flag, for example, may be 00000000 to designatean odd field and 11111111 to designate an even field.

The next forty-eight bits contain the map and comprise, in order, theninth E-VSB data bit E-VSB8, the first map bit, the tenth E-VSB data bitE-VSB9, the second map bit, . . . , the thirty-second E-VSB data bitE-VSB31, and the twenty-fourth map bit. The map, for example, may betwenty four bits that designate which segments in the field will containE-VSB data and which segments in the field will contain VSB data. Thisarrangement implies that twenty-four bits are used for the map.

The remaining bits in the first packet contain alternating E-VSB bitsand place holder bits.

A subsequent E-VSB packet to be inserted in the transmission field ofFIG. 1 is shown in FIG. 5 as a subsequent E-VSB packet 62. Thesubsequent E-VSB packet 62 includes the header described above, exceptthat the last three bytes designate that the subsequent E-VSB packet 62is to be inserted in a subsequent segment of the transmission field ofFIG. 1. The remaining bits in the subsequent E-VSB packet 62 containalternating E-VSB bits and place holder bits. Each of the remainingE-VSB packets to be inserted in the field of FIG. 1 may have theconstruction of the subsequent E-VSB packet 62.

When ½ rate encoding is to be applied to the E-VSB data by the RFtransmitter 22, two 188 byte packets are produced by the E-VSBpreprocessor 40 for each 188 byte packet that is input to the E-VSBpreprocessor 40. Because ½ rate encoding doubles the number of bits inthe data to be encoded, the place holder bits as well as the odd/evenfield flag byte and the three map bytes provide places for these extrabits. The odd/even field flag byte and the three map bytes are used bythe RF transmitter 22 to designate the transmission field (odd or even)and the segments in that transmission field to insert the correspondingE-VSB data and are then discarded to make room for the extra bitsresulting from the ½ rate encoding.

On the other hand, when a coding rate of ¼ is to be applied to the E-VSBdata by the RF transmitter 22, four 188 byte packets are produced by theE-VSB preprocessor 40 for each 188 byte packet that is input to theE-VSB preprocessor 40. Therefore, three place holder bits are requiredfor each E-VSB bit to be encoded. Because ¼ rate encoding quadruples thenumber of encoded data bits, these place holder bits as well as theodd/even field flag byte and the three map bytes provide places forthese extra bits. Again, the odd/even field flag byte and the three mapbytes are used by the RF transmitter 22 to designate the transmissionfield (odd or even) and the segments in that transmission field toinsert the corresponding E-VSB data and are then discarded to make roomfor the extra bits resulting from the ¼ rate encoding. When a codingrate of ¾ is used, one place holder bit may be used after threeconsecutive E-VSB bits.

As indicated above, the mux 38 of FIG. 3, operating in accordance withthe map that is to be inserted into the first segment of a transmissionfield, multiplexes the E-VSB data packets from the E-VSB preprocessor 40with VSB data packets from the VSB buffer 34. The mux 38 then suppliesthe multiplexed packets to an SMPTE encoder 42 that provides thesynchronous data link signal over the serial synchronous data link 20.An SDL frame may be defined by the synchronous data link signal 20 andhas the construction shown in FIG. 6. The SDL frame is provided to theRF transmitter 22 which converts the SDL frame to an odd transmissionfield or an even transmission field.

The first packet in the SDL frame is arranged according to the firstE-VSB packet 60 of FIG. 5. Each of the remaining E-VSB packets in theSDL frame is arranged according to the subsequent E-VSB packet 62 ofFIG. 5. VSB packets may be added as shown by the example of FIG. 6. TheE-VSB packets and the VSB packets are interspersed through the SDL frameaccording to the map. (As indicated above, the SDL frame of FIG. 6 willbe converted by the RF transmitter 22 to the transmission field shown inFIG. 1. As part of the conversion process, the map data will be insertedinto the reserved portion of the field sync segment. Each data packetwill be inserted into one or more of the data segments of an odd or eventransmission field according to the odd/even field flag which will thenbe discarded.)

Modifications of the present invention will occur to those practicing inthe art of the present invention. For example, as described above, theE-VSB packets stored in the E-VSB packet buffer 36 are first processedby an E-VSB preprocessor 40 before being supplied to the mux 38. Ifadditional coding rates are used for E-VSB data, correspondingadditional E-VSB preprocessors may be used, each operating in accordancewith a particular one of coding rates.

Accordingly, the description of the present invention is to be construedas illustrative only and is for the purpose of teaching those skilled inthe art the best mode of carrying out the invention. The details may bevaried substantially without departing from the spirit of the invention,and the exclusive use of all modifications which are within the scope ofthe appended claims is reserved.

1. A method of providing a synchronous data link signal including firstdata to be encoded at a first data rate, second data to be encoded at asecond data rate less than the first data rate, and map data definingthe relative amounts and placement of the encoded first and second datain the synchronous data link signal, the method comprising: providingthe first data in the form of first output data packets of apredetermined size; multiplexing the second data and the map data toprovide more than one second output data packet having the predeterminedsize; and, multiplexing the first and second output data packets toprovide the synchronous data link signal.
 2. The method of claim 1wherein the synchronous data link signal defines an SDL frame, whereinthe SDL frame is to be converted into a transmission field, wherein thetransmission field may be odd or even, and wherein the multiplexing ofthe second data and the map data comprises multiplexing the second data,the map data, and an odd/even field flag having an odd state todesignate that the corresponding second data is to be included in thetransmission field if the transmission field is odd or an even state todesignate that the corresponding second data is to be included in thetransmission field if the transmission field is even.
 3. The method ofclaim 2 wherein the multiplexing of the second data, the map data, andthe odd/even field flag comprises multiplexing the second data, the mapdata, the odd/even field flag, and place holding data to provide themore than one second output data packet.
 4. The method of claim 1wherein the multiplexing of the second data and the map data comprisesmultiplexing the second data, the map data, and place holding data toprovide the more than one second output data packet.
 5. The method ofclaim 1 wherein the multiplexing of the second data and the map datacomprises Reed/Solomon encoding and interleaving the second data.
 6. Themethod of claim 5 wherein the synchronous data link signal defines anSDL frame, wherein the SDL frame is to be converted into a transmissionfield, wherein the transmission field may be odd or even, and whereinthe multiplexing of the second data and the map data comprisesmultiplexing the second data, the map data, and an odd/even field flaghaving an odd state to designate that the corresponding second data isto be included in the transmission field if the transmission field isodd or an even state to designate that the corresponding second data isto be included in the transmission field if the transmission field iseven.
 7. The method of claim 6 wherein the multiplexing of the seconddata, the map data, and the odd/even field flag comprises multiplexingthe second data, the map data, the odd/even field flag, and placeholding data to provide the more than one second output data packet. 8.The method of claim 5 wherein the multiplexing of the second data andthe map data comprises multiplexing the second data, the map data, andplace holding data to provide the more than one second output datapacket.
 9. A method of providing a synchronous data link signalincluding first data to be encoded at a first data rate, second data tobe encoded at a second data rate less than the first data rate, and mapdata defining the relative amounts and placement of the first and seconddata in an SDL frame, the method comprising: providing the first data inthe form of first output data packets of a predetermined size;multiplexing the second data and the map data to provide more than onesecond output data packet having the predetermined size; adding a headerto each of the second output data packets; and, multiplexing the firstand second output data packets to provide the synchronous data linksignal, wherein the header uniquely identifies one of the second outputdata packets.
 10. The method of claim 9 wherein the multiplexing of thesecond data and the map data comprises multiplexing the second data, themap data, and an odd/even field flag to provide the more than one secondoutput data packet, wherein the SDL frame is to be converted into atransmission field, wherein the transmission field may be odd or even,and wherein the odd/even field flag has an odd state to designate thatthe corresponding second data is to be included in the transmissionfield if the transmission field is odd or an even state to designatethat the corresponding second data is to be included in the transmissionfield if the transmission field is even.
 11. The method of claim 10wherein the multiplexing of the second data, the map data, and theodd/even field flag comprises multiplexing the second data, the mapdata, the odd/even field flag, and place holding data to provide themore than one second output data packet.
 12. The method of claim 9wherein the multiplexing of the second data and the map data comprisesmultiplexing the second data, the map data, and place holding data toprovide the more than one second output data packet.
 13. The method ofclaim 9 wherein the multiplexing of the second data and the map datacomprises Reed/Solomon encoding and interleaving the second data. 14.The method of claim 13 wherein the multiplexing of the second data andthe map data comprises multiplexing the second data, the map data, andan odd/even field flag to provide the more than one second output datapacket, wherein the SDL frame is to be converted into a transmissionfield, wherein the transmission field may be odd or even, and whereinthe odd/even field flag has an odd state to designate that thecorresponding second data is to be included in the transmission field ifthe transmission field is odd or an even state to designate that thecorresponding second data is to be included in the transmission field ifthe transmission field is even.
 15. The method of claim 14 wherein themultiplexing of the second data, the map data, and the odd/even fieldflag comprises multiplexing the second data, the map data, the odd/evenfield flag, and place holding data to provide the more than one secondoutput data packet.
 16. The method of claim 13 wherein the multiplexingof the second data and the map data comprises multiplexing the seconddata, the map data, and place holding data to provide the more than onesecond output data packet.
 17. A method of providing a synchronous datalink signal including first packets of first data to be encoded at afirst data rate, second packets of second data to be encoded at a seconddata rate less than the first data rate, and map data defining therelative amounts and placement of the encoded first and second data inthe synchronous data link signal, wherein each of the first packets hasa first size, wherein each of the second packets has a second size,wherein the first and second sizes are equal, the method comprising:splitting the second packets into packet portions each having a thirdsize, wherein the third size is less than the second size; adding datato the packet portions to create third packets, wherein each of thethird packets has a size, wherein the size of each of the third packetsis equal to the second size, and wherein the data added to the packetportions includes header data; and, multiplexing the first packets, thethird packets, and the map data to provide the synchronous data linksignal.
 18. The method of claim 17 wherein the synchronous data linksignal defines an SDL frame, wherein the SDL frame is to be convertedinto a transmission field, wherein the transmission field may be odd oreven, and wherein the multiplexing comprises multiplexing the third datapackets, the map data, and an odd/even field flag having an odd state todesignate that the corresponding third packets are to be included in thetransmission field if the transmission field is odd or an even state todesignate that the corresponding third packets are is to be included inthe transmission field if the transmission field is even.
 19. The methodof claim 18 wherein the multiplexing comprises multiplexing the thirddata packets, the map data, and place holding data to provide thesynchronous data link signal.
 20. The method of claim 17 wherein themultiplexing comprises multiplexing the third data packets, the mapdata, and place holding data to provide the synchronous data linksignal.
 21. The method of claim 17 wherein the data added to the packetportions further includes Reed/Solomon data.
 22. The method of claim 17wherein the multiplexing comprises multiplexing the first packets, thethird packets, and the map data as an SDL frame, and wherein the methodfurther comprises converting the SDL frame to an ATSC digital televisionstandard transmission field.
 23. The method of claim 22 wherein the ATSCdigital television standard transmission field may be odd or even, andwherein the multiplexing of the first packets, the third packets, andthe map data as an SDL frame comprises multiplexing the first packets,the third packets, the map data, and an odd/even field flag having anodd state to designate that the corresponding third packets are to beincluded in the ATSC digital television standard transmission field ifthe ATSC digital television standard transmission field is odd or aneven state to designate that the corresponding third packets are to beincluded in the ATSC digital television standard transmission field ifthe ATSC digital television standard transmission field is even.